像陡峭山坡上的雪崩一样，一束入射光的脉冲最初仅仅释放少数的电荷载子(charge carrier)，这些电荷载子再轮流释放其他的载子，直到原始信号被放大很多次。
Analogous to a snow avalanche on a steep mountain slope, an incoming light pulse initially frees just a few charge carriers which in turn free others until the original signal is amplified many times.
但反射式就不能像入射式如实反映各主体表面的反射比率。
But reflected type may not reflect the true reflectance of subject surfaces like incident type meters.
激光束垂直入射到火车车轮上，再用透镜将火车车轮上的激光光斑成像到CCD上，当火车车轮产生磨损时，CCD上激光光斑的像也将发生位移。
The laser spot of the upright incidence to train wheel is imaged on CCD. While the train wheels are frayed, the image of spot will take place displacement.
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